Controlled or timed release is primarily a technique for the control of the rate of delivery of a chemical substance. Release of a chemical substance over time is widely used in connection with pharmaceuticals, pesticides, herbicides, and fertilizers and also in many other cases where a particular chemical agent must be administered on a periodic or sustained basis.
During the last several decades, many different technologies for the controlled release of chemical substances have been developed: encapsulation, entrapment, osmotic pumps, reservoirs, soluble glasses and erosible/degradable matrices. While suitable techniques for the time release of a great number of specific chemical agents (organic as well as inorganic) are available no practical, more generally applicable system is available for any of the permanganates, a family of strong oxidizing agents.
Water soluble salts of permanganic acid, such as KMnO.sub.4, are sold for a great variety of uses: organic synthesis, organic solvent purification, water, waste water and air purification, metal surface treatment, the etching of plastics and numerous other applications. In many of these use areas, the permanganate must be added at a controlled rate to produce a predetermined concentration range which avoids underdosing and overdosing. The controlled addition is usually achieved by employing mechanical feeding devices for either the dry product or its aqueous solution. Mechanical feeding devices, however, require the availability of electric power at the point of use for the operation of feeders. This availability requirement can be a problem in certain environmental uses of permanganate such as odor (H.sub.2 S) abatement in sewer collection lines. In this and many other applications such as water treatment, it would be highly advantageous to have a suitably formulated product available that is designed to release permanganate ion at the required predetermined rate without the benefit of any mechanical/electric dosing equipment.
When addressing the problem of developing a controlled release permanganate, it becomes quickly apparent that the oxidative and corrosive properties of permanganate preclude the use of many of the materials customarily used in the preparation of time release formulations. Thus, for all practical purposes, practically all organics such as encapsulants, matrix materials or coatings are not useable, as are all oxidizable inorganics.
It is an object of this invention to provide a composition which releases permanganate ion at a controlled or timed rate in an aqueous media.
Another object of this invention is to make a layered cementitious composition which includes a concentration of permanganate at its core, but is substantially free of permanganate at its surface.
It is yet another object of this invention to provide a method for the controlled release of permanganate ion in an aqueous media.
These and other objects and advantages of the invention will be found by reference to the following description.